System and method for fast network re-entry in a broadband wireless access communication system

ABSTRACT

A system and method for fast network re-entry in a broadband wireless access communication system. A mobile station transmits a first message requiring fast network re-entry to a base station and performs the fast network re-entry together with the base station when receiving a second message approving the fast network re-entry from the base station. The base station receives the first message, authenticates the first message using final session information of the mobile station that is previously stored in the base station, transmits the second message to the mobile station when succeeding in authentication of the first message, and performs the fast network re-entry together with the mobile station.

PRIORITY

This application claims priority under 35 U.S.C. § 119 to applicationsentitled “System And Method For Fast Network Re-entry In BroadbandWireless Access Communication System” filed in the Korean IndustrialProperty Office on Jun. 11, 2004 and assigned Serial No. 2004-43232, andon Jun. 25, 2004 and assigned Serial No. 2004-48568, the contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a system and method forBroadband Wireless Access (BWA) communication, and more particularly toa system and method, by which a mobile station (MS) in an idle stateperforms fast network re-entry using final session information of aprevious active state in a BWA communication system.

2. Description of the Related Art

In the next generation communication system, research has been activelypursued to provide users with services having various qualities ofservices (QoSs) and supporting a high transmission speed. Morespecifically, for the next generation communication system, research hasbeen actively pursued to develop a new type of communication systemensuring mobility and QoS in a BWA communication system such as awireless Local Area Network (LAN) system and a wireless MetropolitanArea Network (MAN) system capable of supporting relatively hightransmission speeds. For example, an Institute of Electrical andElectronics Engineers (IEEE) 802.16e communication system has beendeveloped. The IEEE 802.16e communication system is an improvement ofthe IEEE 802.16d communication system in that IEEE 802.16e communicationsystem is provided with mobility in addition to the structure of theIEEE 802.16d communication system, which provides broadband Internetservice to a stationary Subscriber Station (SS).

As described above, the IEEE 802.16d communication system does notprovide mobility at all because it is a communication system forproviding broadband Internet service to a stationary SS. However,although the IEEE 802.16e communication system handles mobility, it isstill in a very poor state for supporting various service functions suchas a security function.

In the IEEE 802.16e communication system, transition into an idle stateis frequently performed in order to minimize power consumption of aMobile Station (MS). Further, the IEEE 802.16e communication systemsupports handover of the MS and the MS must perform network re-entry orlocation registration when the handover is performed. In this case, callsetup must be re-performed between the Base Station (BS) and the MS andsession information for the active state of the MS must regenerated.That is, for handover of the MS in the idle state, the MS must eitherperform the location registration or perform network re-entry process inorder to transit from the idle state to an active state. The locationregistration or the network re-entry process causes processing delay andincreases message signaling load.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been designed to solve the aboveand other problems occurring in the prior art. An object of the presentinvention is to provide a system and method for fast network re-entry ina BWA communication system.

It is another object of the present invention to provide a system andmethod by which an MS in an idle state performs fast network re-entryusing final session information in a BWA communication system.

In order to accomplish the above and other objects, there is provided amethod for fast network re-entry of a mobile station in a broadbandwireless access communication system. The method comprises the steps of:transmitting a first message requesting fast network re-entry to a basestation when the mobile station detects that it is necessary to performnetwork re-entry to the base station in an idle state in which themobile station stores final session information of a previous activestate; receiving a second message approving the fast network re-entryfrom the base station; and performing the fast network re-entry with thebase station.

In accordance with another aspect of the present invention, there isprovided a method for fast network re-entry of a mobile station in abroadband wireless access communication system including the mobilestation, a serving base station that provides service to the mobilestation, a target base station, which is different from the serving basestation, and an ASA (Authentication and Service Authorization) serverconnected to the target base station. The method comprises the steps ofstoring final session information by the mobile station whentransitioning into an idle state; transmitting the final sessioninformation to the target base station so that the target base stationand the ASA server store the final session information, when the mobilestation detects that handover from the serving base station to thetarget base station is necessary, after the mobile station stores thefinal session information; transmitting a first message requiring fastnetwork re-entry to the target base station; receiving a second messageapproving the fast network re-entry from the target base station; andperforming the fast network re-entry with the target base station.

In accordance with another aspect of the present invention, there isprovided a method for fast network re-entry of a base station in abroadband wireless access communication system. The method comprises thesteps of: receiving a first message requiring fast network re-entry froma mobile station that is in an idle state during which the mobilestation stores final session information of a previous active state;authenticating the first message using final session information of themobile station that is previously stored in the base station;transmitting a second message approving the fast network re-entry to themobile station, after the first message is authenticated; and performingthe fast network re-entry with the mobile station.

In accordance with another aspect of the present invention, there isprovided a method for fast network re-entry in a broadband wirelessaccess communication system. The method comprises the steps of:transmitting a first message requiring fast network re-entry from amobile station to a base station, when the mobile station detects thatit is necessary to perform network re-entry to the base station in anidle state during which the mobile station stores final sessioninformation of a previous active state; receiving the first message bythe base station; authenticating the first message by the base stationusing final session information of the mobile station that is previouslystored in the base station; transmitting a second message approving thefast network re-entry to the mobile station, the first message isauthenticated; and performing the fast network re-entry by the mobilestation and the base station.

In accordance with another aspect of the present invention, there isprovided a method for fast network re-entry in a broadband wirelessaccess communication system that includes the mobile station, a servingbase station that provides service to the mobile station, a target basestation, which is different from the serving base station, and an ASA(Authentication and Service Authorization) server connected to thetarget base station. The method comprises the steps of: transmittingfinal session information from the mobile station to the target basestation so that the target base station and the ASA server store thefinal session information, when the mobile station detects that handoverfrom the serving base station to the target base station is necessary,after the mobile station stores the final session information whiletransitioning into an idle state; receiving the final sessioninformation in the target base station; storing the final sessioninformation in the target base station; transmitting a first messagerequiring the fast network re-entry to the target base station;receiving the first message by the target base station; authenticatingthe first message by the target base station using final sessioninformation of the mobile station stored in advance in the target basestation; transmitting a second message approving the fast networkre-entry to the mobile station, after authenticating the first message;and performing the fast network re-entry by the mobile station and thetarget base station.

In accordance with another aspect of the present invention, there isprovided a system for fast network re-entry in a broadband wirelessaccess communication system. The system comprises a base station; and amobile station for transmitting a first message requiring fast networkre-entry to the base station when the mobile station detects that it isnecessary to perform network re-entry to the base station in an idlestate during which the mobile station stores final session informationof a previous active state, the mobile station performing the fastnetwork re-entry together with the base station when receiving a secondmessage approving the fast network re-entry from the base station,wherein the base station receives the first message, authenticates thefirst message using final session information of the mobile station thatis previously stored in the base station, transmits the second messageto the mobile station, after authenticating the first message, andperforms the fast network re-entry with the mobile station.

In accordance with another aspect of the present invention, there isprovided a system for fast network re-entry in a broadband wirelessaccess communication system. The system comprises a target base station;and a mobile station for storing final session information whentransitioning into an idle state, transmitting the final sessioninformation to the target base station, such that the target basestation and an ASA (Authentication and Service Authorization) serverstore the final session information, when the mobile station detectsthat handover from a serving base station to the target base station isnecessary after the mobile station stores the final session information,transmitting a first message requiring fast network re-entry to thetarget base station, and performing the fast network re-entry with thetarget base station, when receiving a second message approving the fastnetwork re-entry from the target base station; wherein the target basestation receives and stores the final session information, authenticatesthe first message using final session information of the mobile stationstored in advance in the target base station, transmits the secondmessage to the mobile station, after authenticating the first message,and performs the fast network re-entry together with the mobile station.

In accordance with another aspect of the present invention, there isprovided a method for fast network re-entry of a base station in abroadband wireless access communication system, the method comprisingthe steps of: transmitting to a mobile station in an active state aderegistration command message to request for transition into an idlestate, wherein the deregistration command message includes sessioninformation for a fast network re-entry; receiving a ranging requestmessage from the mobile station to perform the network re-entry afterthe mobile station transit into the active state; transmitting to themobile station a ranging response message which includes the sessioninformation represents whether each network re-entry process amongnetwork re-entry procedure is omitted or required.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 schematically illustrates a message format of a DREG-CMD messageaccording to an embodiment of the present invention;

FIG. 2 is a signal flow diagram illustrating a process of authenticatingthe LU-REQ message of the MS according to an embodiment of the presentinvention;

FIG. 3 illustrates a table of the LU-REQ message according to anembodiment of the present invention;

FIG. 4 is a signal flow diagram illustrating a process of fast networkre-entry according to an embodiment of the present invention;

FIG. 5 illustrates a table of the RNG-REQ message according to anembodiment of the present invention;

FIG. 6 illustrates a table of the RNG-RSP message according to anembodiment of the present invention;

FIG. 7 illustrates a table of the MOB-PAG-ADV message according to anembodiment of the present invention;

FIG. 8 is a signal flow diagram illustrating a process of SAID/TCIDmapping and dynamic service for each service flow according to anembodiment of the present invention;

FIG. 9 is a signal flow diagram illustrating a fast network re-entryprocess according to an embodiment of the present invention;

FIG. 10 is a signal flow diagram of a network re-entry process when theBS pages the MS in the idle state according to an embodiment of thepresent invention;

FIG. 11 illustrates a table of the RNG-REQ message according to anembodiment of the present invention;

FIG. 12 illustrates a table of the RNG-RSP message according to anembodiment of the present invention; and

FIG. 13 illustrates a table of the MOB-PAG-ADV message according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of the present invention will be described indetail herein below with reference to the accompanying drawings. In thefollowing description, the same elements will be designated by the samereference numerals although they are shown in different drawings.Further, in the following description of the present invention, adetailed description of known functions and configurations incorporatedherein will be omitted when it may obscure the subject matter of thepresent invention.

The present invention proposes a system and method by which a MobileStation (MS) in an idle state performs fast network re-entry usingsession information of a previous final active state in a BroadbandWireless Access (BWA) communication system. In the followingdescription, an Institute of Electrical and Electronics Engineers (IEEE)802.16e communication system is discussed as an example of the BWAcommunication system. However, it should be noted that the fast networkre-entry system and method proposed by the present invention can beapplied to other communication systems as well.

Before describing the present invention, a Session Information Record(SIR) will be first defined.

When an MS transitions from an active state to an idle state, the MSreleases all Medium Access Control (MAC) connections, such as a basicconnection and a primary connection in the active state, and deletessecurity-associated information stored in the memory of the MS itself.

The SIR refers to minimum information, which must be stored by the MSand a system, e.g. a BS or an authentication server, in order to supporta Reduced Call Setup (RCS), which defines fast transition from the idlestate to the active state or location update when the MS performs idlehandover. Hereinafter, the SIR will be described in detail.

An SIR includes a MAC address of the MS, an SIR identifier (SIR ID), aMAC version/Internet Protocol (IP) version/IP address, a Base Station(BS) identifier (BS ID) or an Authentication and Service ASA server ID(ASID), authentication information, and Subscriber Station (SS) callsession information of Type, Length, Value (TLV) format.

The MAC address and the SIR ID are identifiers for identifying the SIR,so that the SIR can be identified by the MAC address and the SIR ID evenwhen the connection information of the MS stored in the BS has beendiscarded due to the transition of the MS into the idle state. Theauthentication information includes an Authorization Key (AK) providedwhen authentication between the MS and the BS is accomplished, anavailable period of the AK, a Keyed-Hashing for Message AuthenticationCode (HMAC) tuple generated using an HMAC algorithm and the AK by the MSand the BS, and an available period of the HMAC tuple.

The SS call session information includes service flow information of aminimum physical layer (PHY), a MAC and each service instance, which arenecessary in order for the MS in the idle state to receive or transmitthe packet data. The SS call session information is used when the RCS isperformed between the MS and the BS or when the location registration inthe idle handover is performed.

The SS call session information includes an SS basic capability uploadedby the MS, an actual basic capability of the MS, an Automatic RetransmitRequest (ARQ) parameter uploaded by the MS, a granted ARQ parameter ofthe MS, convergence capabilities uploaded by the MS, granted convergencecapabilities and service flow information of the MS, security-associatedinformation for each service flow except for Service Association ID(SAID) and Transport Connect ID (TCID), a Subscriber station's BasicCapability negotiation request (SBC-REQ) message, and basic capabilitynegotiation parameters of the MS negotiated through a Subscriberstation's Basic Capability negotiation response (SBC-RSP) message, whichis a response to the SBC-REQ message.

The MS and the BS determine whether or not to store the SIR. Whentransitioning into the idle state, it is unnecessary for the MS or theBS to require or report storage of the SIR to the counterpart. Further,the information on whether to generate the SIR may be reported to the MSthrough an SIR_ID_INCL Information Element (IE) indicating inclusion orexclusion of an SIR identifier in a DeRegistration-Command (DREG-CMD)message, which is a MAC management message transmitted from the BS tothe MS in response to a request of the MS for transition into the idlestate transmitted from the MS to the BS. The SIR basically uses finalsession information. Here, the DREG-CMD message, which is a messagenewly proposed by the present invention, is generated by modifying theformat of the DREG-CMD message of the typical IEEE 802.16e communicationsystem. Alternatively, the DREG-CMD message according to an embodimentof the present invention may be generated with a totally new formatinstead of being generated by changing the format of the DREG-CMDmessage of the typical IEEE 802.16e communication system.

FIG. 1 schematically illustrates a message format of a DREG-CMD messageaccording to an embodiment of the present invention. Referring to FIG.1, the DREG-CMD message includes a plurality of IEs such as SIR_ID_INCLand SIR_ID. The SIR_ID_INCL indicates if the DREG-CMD message includesthe SIR ID and the SIR_ID indicates the SIR ID when the SIR_ID_INCLindicates that the DREG-CMD message includes the SIR ID. The SIR ID isused to determine if the SIR stored in the MS coincides with the SIRstored in the BS, when the MS performs location update or RCS using theSIR.

The SIR is maintained during a predetermined time interval even when thelocation of the MS has changed or when the MS moves to a region ofanother BS or SIR management server due to network re-entry, etc.Thereafter, when the MS stays in the idle state and does not transit tothe active state during the maintenance interval, the SIR is deleted.However, when the MS transitions from the idle state to the active stateor the context of the SIR changes within the maintenance interval, themaintenance time interval is set again such that the SIR can bemaintained during the reset maintenance interval. Further, when thepower supply to the MS is interrupted, the SIR is deleted from the MSand the power interruption is reported to the system through thelocation update. Further, when the information included in the SIR ischanged by the MS and the BS, the stored SIR is also updated instantly.

When the MS performs handover in the idle state, all MAC connections arereleased and security-associated information is deleted, such that it isimpossible to authenticate a Location Update Request (LU-REQ) messageaccording to the handover of the MS. Therefore, in order to authenticatethe LU-REQ message transmitted from the MS, it is required that a targetBS to which the handover of the MS is oriented should request the SIR ofthe MS from a serving BS of the MS or an Authentication and ServiceAuthorization (ASA) server and receive the SIR of the MS correspondingto the request from the serving BS or the ASA server.

Hereinafter, authentication of the LU-REQ message of the MS will bebriefly described.

First, the MS authenticates the LU-REQ message using an HMAC tuple,which is generated using an authorization key included in the SIR storedin the MS itself, and transmits the authenticated LU-REQ message to thetarget BS to which the handover is destined. Then, the target BSreceives the LU-REQ message transmitted from the MS, requests the SIR ofthe MS to the serving BS of the MS or the ASA server according to thereception of the LU-REQ message, and then receives the SIR of the MSfrom the serving BS of the MS or the ASA server. After receiving the SIRof the MS in this way, the target BS authenticates the LU-REQ messageusing the received SIR of the MS.

FIG. 2 is a signal flow diagram illustrating a process of authenticatingthe LU-REQ message of the MS according to an embodiment of the presentinvention. Referring to FIG. 2, the MS 200 scans neighbor BSs anddetermines to perform handover from a serving BS from which the MS 200currently receives service to a target BS 240, which is one of thescanned neighbor BSs, in step 211. Here, the operation in relation tothe scanning and determination of handover has no direct relation to thepresent invention. Therefore, a detailed description thereof will beomitted here.

After determining the handover to the target BS 240, the MS 200transmits the LU-REQ message to the target BS 240 in step 213. However,before transmitting the LU-REQ message, the MS 200 authenticates theLU-REQ message based on the authentication information in the SIR storedin advance in the MS. The LU-REQ message includes the ASID of the ASAserver 260 connected to the MS 200.

FIG. 3 illustrates a table of the LU-REQ message according to anembodiment of the present invention. Referring to FIG. 3, the LU-REQmessage includes a plurality of IEs such as ASID, AK, AK lifetime, HMACTuple, HMAC Tuple lifetime, and RCS Request, which indicates whether thecorresponding MS requires the RCS, in accordance with the TLV format.The LU-REQ message in FIG. 3 is a message newly proposed by the presentinvention and is generated by modifying the format of the LU-REQ messageof the typical IEEE 802.16e communication system. Alternatively, theLU-REQ message according to an embodiment of the present invention maybe generated with a totally new format, instead of being generated bymodifying the format of the LU-REQ message of the typical IEEE 802.16ecommunication system.

Referring back to FIG. 2, the target BS 240 receives the LU-REQ messagefrom the MS 200 and detects the ASID from the received LU-REQ message.Then, the target BS 240 transmits a Session Information Record Request(SIR-REQ) message requiring the SIR of the MS 200 to the ASA server 260in step 215. The SIR-REQ message includes a MAC address that is anidentifier of the MS 200.

Upon receiving the SIR-REQ message from the target BS 240, the ASAserver 260 detects the SIR of the MS 200 corresponding to the MACaddress included in the SIR-REQ message from the database constructed inthe ASA server 260. Further, the ASA server 260 inserts the detected SIRof the MS 200 in a Session Information Record Response (SIR-RSP) messageand transmits the SIR-RSP message to the target BS 240, as a response tothe SIR-REQ message, in step 217.

The target BS 240 receives the SIR-RSP message from the ASA server 260,detects the SIR of the MS 200 from the received SIR-RSP message, andauthenticates the LU-REQ message by using the HMAC Tuple in the detectedSIR in step 250. Upon succeeding in the authentication of the LU-REQmessage, the target BS 240 transmits the LU-RSP message to the MS 200 asa response to the LU-REQ message in step 221.

When the location update according to idle handover of the MS isperformed as described above, the SIR of the MS controlled by theserving BS of the MS or the higher class server, i.e., theAuthentication and Service Authorization (ASA) server, is transferred toa new serving BS, i.e., the target BS or a new ASA server. Thereafter,in the network re-entry process, it is unnecessary for the BS to performsome operations such as acquisition of SIR or authentication of amessage, such that the MS can achieve fast network re-entry.

FIG. 4 is a signal flow diagram illustrating a process of fast networkre-entry according to an embodiment of the present invention. Morespecifically, the fast network re-entry process illustrated in FIG. 4corresponds to a fast network re-entry process after the location updateaccording to the idle handover of the MS is performed as describedabove.

Referring to FIG. 4, the MS 400 stays in the idle state in step 411 andthen transmits a ranging request (RNG-REQ) message to the BS, which isthe target BS in step 413. The RNG-REQ message is a message newlyproposed by the present invention and is generated by modifying theformat of the RNG-REQ message of the typical IEEE 802.16e communicationsystem. Alternatively, the RNG-REQ message according to an embodiment ofthe present invention may be generated with a totally new format,instead of being generated by modifying the format of the RNG-REQmessage of the typical IEEE 802.16e communication system.

FIG. 5 illustrates a table of the RNG-REQ message according to anembodiment of the present invention. Referring to FIG. 5, the RNG-REQmessage includes a plurality of IEs such as RCS Request, Request Type,SIR identifier, and ASID in accordance with the TLV format. Here, theRequest Type has a length of one byte, i.e., 8 bits. When the first bit(bit #0) from among the 8 bits of the Request Type has a value of 1, itimplies that the RCS is requested.

The BS 420 receives the RNG-REQ message and detects the SIR ID from thereceived RNG-REQ message. The BS 420 determines if an SIR correspondingto the detected SIR ID exists in the database of the BS 420. When no SIRcorresponding to the detected SIR ID exists in the database of the BS420, the BS transmits the SIR-REQ message to the ASA server 440, whichis an ASA server corresponding to the ASID included in the receivedRNG-REQ message in step 415. The SIR-REQ message includes an SIR ID anda MAC address, which is an identifier of the MS 400.

Upon receiving the SIR-REQ message from the BS 420, the ASA server 440detects the SIR of the MS 400 corresponding to the SIR ID and the MACaddress included in the SIR-REQ message from the database in the ASAserver 440. Then, the ASA server 440 inserts the detected SIR of the MS400 in an SIR-RSP message and transmits the SIR-RSP message to the BS420 as a response to the SIR-REQ message in step 417.

When an SIR corresponding to the detected SIR ID exists in the databaseof the BS 420, transmission of the SIR-REQ message and reception of theSIR-RSP message are omitted. The BS 420 detects the SIR from the SIR-RSPmessage and authenticates the RNG-REQ message in accordance with theHAMC Tuple of the detected SIR. Upon authenticating the RNG-REQ message,the BS 420 transmits a ranging response (RNG-RSP) message to the MS 400as a response to the RNG-REQ message in step 419. The RNG-RSP message isa message newly proposed by the present invention and is generated bymodifying the format of the RNG-RSP message of the typical IEEE 802.16ecommunication system. Alternatively, the RNG-RSP message according to anembodiment of the present invention may be generated with a totally newformat, instead of being generated by modifying the format of theRNG-RSP message of the typical IEEE 802.16e communication system.

FIG. 6 illustrates a table of the RNG-RSP message according to anembodiment of the present invention. Referring to FIG. 6, the RNG-RSPmessage includes a plurality of lEs such as RCS Response, Response Typeand ASID in accordance with the TLV format. The Response Type has alength of one byte, i.e., 8 bits. When the first bit (bit #0) from amongthe 8 bits of the Response Type has a value of 1, it indicates that theRCS has been totally accepted (‘Reduced Call Setup totally accepted’).When the second bit (bit #1) from among the 8 bits of the Response Typehas a value of 1, it indicates that the RCS has been rejected and the MSis forced to perform a normal network entry procedure (‘Reduced callSetup Rejected and SS is forced to perform a normal network entryprocedure’). When the third bit (bit #2) has a value of 1, it indicatesthat SS Basic Capability (SBC) re-negotiation is required (‘SS BasicCapability (SBC) re-negotiation required’). When the fourth bit (bit #3)has a value of 1, it indicates that Privacy Key Management (PKM)re-negotiation is required (‘Privacy Key Management (PKM) re-negotiationrequired’). When the fifth bit (bit #4) has a value of 1, it indicatesthat Registration (REG) re-negotiation is required (‘Registration (REG)re-negotiation required’). When the sixth bit (bit #5) has a value of 1,it indicates that Internet Protocol (IP) re-allocation is required(‘Internet Protocol (IP) re-allocation required’). Further, although notillustrated in FIG. 6, the RNG-RSP message includes an ASID, a basic CIDallocated to the MS 400, and a primary CID.

As the MS 400 receives the RNG-RSP message from the BS 420, it ispossible to omit the SBC negotiation procedure, which includes SBC-REQmessage transmission and SBC-RSP reception, the Privacy Key Management(PKM) procedure, which includes Privacy Key Management Request (PKM-REQ)message transmission and Privacy Key Management Response (PKM-RSP)message reception, and the registration procedure, which includesRegistration Request (REG-REQ) message transmission and RegistrationResponse (REG-RSP) message reception, during the existing networkre-entry process. As a result, it is possible to perform fast networkre-entry.

However, in order to refresh the privacy key value, a one time PKM-REQmessage transmission and the PKM-RSP message reception is performed,instead of performing an at least three time PKM-REQ messagetransmission and the PKM-RSP message reception as in the typical networkre-entry process. That is, the MS 400 transmits the PKM-REQ message tothe BS 420 in step 421.

Upon receiving the PKM-REQ message from the MS 400, the BS 420 transmitsthe PKM-REQ message to the ASA server 440 in step 423. The ASA server440 transmits the PKM-RSP message to the BS 420, as a response to thePKM-REQ message, in step 425. Upon receiving the PKM-RSP message fromthe ASA server 440, the BS 420 transmits the PKM-RSP message to the MS400 in step 427.

Although FIG. 4 illustrates that the fast network re-entry isaccomplished through the RNG-REQ message transmission and the RNG-RSPmessage reception, it is possible to achieve the fast network re-entrythrough the SBC-REQ message transmission and the SBC-RSP messagereception.

When there is information that the BS wants to change from among thefinal session information stored in the SIR of the BS, the BS enablesthe MS to perform the negotiation only about the correspondinginformation. For example, it is possible to re-perform only the MSauthentication while maintaining setup values of the physical layer, theMAC layer, and the Convergence Sublayer (CS) or to re-negotiate only thesetup values of the CS.

When there is packet data to be transmitted from the BS to the MS, theBS pages the MS using a paging message in which the SIR ID is inserted.

Hereinafter, a format of a Mobile Paging Advertisement (MOB-PAG-ADV)message for paging the MS will be described with reference to FIG. 7. Itis noted that the MOB-PAG-ADV message is a message newly proposed by thepresent invention and is generated by modifying the format of theMOB-PAG-ADV message of the typical IEEE 802.16e communication system.Alternatively, the MOB-PAG-ADV message according to an embodiment of thepresent invention may be generated with a totally new format, instead ofbeing generated by modifying the format of the MOB-PAG-ADV message ofthe typical IEEE 802.16e communication system.

FIG. 7 illustrates a table of the MOB-PAG-ADV message according to anembodiment of the present invention. Referring to FIG. 7, theMOB-PAG-ADV message includes a plurality of lEs such as SIR_ID_INCL andSIR_ID. The SIR_ID_INCL represents if the MOB-PAG-ADV message includesthe SIR ID or not, and the SIR_ID represents the SIR ID when theSIR_ID_INCL represents that the MOB-PAG-ADV message includes the SIR ID.

If the BS stores an SIR having the same SIR ID as the SIR ID that the BSreceived from the MS as described above or if it is possible to acquirethe SIR from the existing authentication server, etc., it is naturallypossible to perform a termination call setup through a process similarto the process in which the MS requests fast network re-entry.

FIG. 8 is a signal flow diagram illustrating a process of SAID/TCIDmapping and dynamic service for each service flow according to anembodiment of the present invention. Referring to FIG. 8, after the MS800 performs the RCS procedure with the BS 820 in step 811, it isnecessary to perform authentication for each service flow when the SIRstores service flows, although not shown in FIG. 8. After authenticatingeach service flow, the BS 820 re-stores the authenticated service flowsin step 813. The MSS 800 transmits a Dynamic Service Add Response(DSA-RSP) message to the BS 820 in an unsolicited manner in step 815.Here, the DSA-RSP message is transmitted in order to reset the dynamicservice for the MS 800 according to each service flow by re-mapping theSAID and TCID.

FIG. 9 is a signal flow diagram illustrating a fast network re-entryprocess according to an embodiment of the present invention. Morespecifically, FIG. 9 is based on an assumption that the shown fastnetwork re-entry process is a process after a previous serving BSregisters the SIR (previous final session information) of the MS 900 inthe ASA server 940 according to transition of the MS 900 into the idlestate, or a process after a previous serving BS registers the SIR(previous final session information) of the MS 900 in the ASA server 940according to handover of the MS 900 or a process after a previousserving BS registers the SIR (previous final session information) of theMS 900 in the ASA server 940 according to location update following thehandover of the MS 900.

Referring to FIG. 9, the MS 900 stays in the idle state in step 911 andthen transmits the RNG-REQ message to the BS 920 in step 913. TheRNG-REQ message is a message newly proposed by the present invention andis generated by modifying the format of the RNG-REQ message of thetypical IEEE 802.16e communication system. Alternatively, the RNG-REQmessage according to an embodiment of the present invention may begenerated with a totally new format, instead of being generated bymodifying the format of the RNG-REQ message of the typical IEEE 802.16ecommunication system.

FIG. 11 illustrates a table of the RNG-REQ message according to anembodiment of the present invention. The RNG-REQ message includes aplurality of lEs such as RCS Request and Request Type in accordance withthe TLV format. Here, the Request Type has a length of one byte, i.e., 8bits, each bit of which has the following meaning.

When the first bit (bit #0) from among the 8 bits of the Request Typehas a value of 1, it indicates that it is possible to omit the SBC-REQmessage transmission and SBC-RSP message reception during the currentnetwork re-entry procedure (‘omit SBC-REQ/RSP management message duringthe current network re-entry processing’). When the second bit (bit #1)has a value of 1, it indicates that it is possible to omit the PKM-REQmessage transmission and PKM-RSP message reception during the currentnetwork re-entry procedure (‘omit PKM-REQ/RSP management messages duringcurrent network re-entry processing’). When the third bit (bit #2) has avalue of 1, it indicates that it is possible to omit the REG-REQ messagetransmission and REG-RSP message reception during the current networkre-entry procedure (‘omit REG-REQ/RSP management messages during currentnetwork re-entry processing’). When the fourth bit (bit #3) has a valueof 1, it indicates that it is possible to omit transmission/reception ofnetwork address acquisition messages during the current network re-entryprocedure (‘omit Network Address Acquisition management messages duringcurrent network re-entry processing’). When the fifth bit (bit #4) has avalue of 1, it indicates that it is possible to omittransmission/reception of time information acquisition messages duringthe current network re-entry procedure (‘omit Time of Day Acquisitionmanagement messages during current network re-entry processing’). Whenthe sixth bit (bit #5) has a value of 1, it indicates that it ispossible to omit transmission/reception of TFTP (Trivial File TransferProtocol) messages during the current network re-entry procedure (‘omitTFTP management messages during current network re-entry processing’).Further, although not illustrated in FIG. 11, the RNG-REQ messageincludes an SIR ID and an ASID in accordance with the TLV format.

Referring back to FIG. 9, the BS 920 examines if an SIR corresponding tothe SIR ID included in the RNG-REQ message from the MS 900 exists in thedatabase of the BS 920. When no SIR corresponding to the detected SIR IDexists in the database of the BS 920, the BS 920 transmits the SIR-REQmessage to the ASA server 940, which is an ASA server corresponding tothe ASID included in the received RNG-REQ message, in step 915. TheSIR-REQ message includes an SIR ID and a MAC address, which is anidentifier of the MS 900.

Upon receiving the SIR-REQ message from the BS 920, the ASA server 940detects the SIR of the MS 900 corresponding to the SIR ID and the MACaddress included in the SIR-REQ message from the database in the ASAserver 940. Then, the ASA server 940 inserts the detected SIR of the MS900 in an SIR-RSP message and transmits the SIR-RSP message to the BS920, as a response to the SIR-REQ message, in step 917.

When an SIR corresponding to the detected SIR ID exists in the databaseof the BS 920, transmission of the SIR-REQ message and reception of theSIR-RSP message are omitted. The BS 920 detects the SIR from the SIR-RSPmessage and authenticates the RNG-REQ message in accordance with theHAMC Tuple of the detected SIR.

Upon succeeding in the authentication of the RNG-REQ message, the BS 920transmits a ranging response (RNG-RSP) message to the MS 900, as aresponse to the RNG-REQ message, in step 919. Herein, the RNG-RSPmessage is a message newly proposed by the present invention and isgenerated by modifying the format of the RNG-RSP message of the typicalIEEE 802.16e communication system. Alternatively, the RNG-RSP messageaccording to an embodiment of the present invention may be generatedwith a totally new format, instead of being generated by modifying theformat of the RNG-RSP message of the typical IEEE 802.16e communicationsystem.

FIG. 12 illustrates a table of the RNG-RSP message according to anembodiment of the present invention. Referring to FIG. 12, the RNG-RSPmessage includes a plurality of IEs such as RCS Response and ResponseType in accordance with the TLV format. Further, although not shown inFIG. 12, the RNG-RSP message includes an ASID, a basic CID allocated tothe MS 900, and a primary CID.

The Response Type has a length of one byte, i.e., 8 bits, each bit ofwhich will be described below.

When the first bit (bit #0) from among the 8 bits of the Response Typehas a value of 1, it indicates that it is possible to omit the SBC-REQmessage transmission and SBC-RSP message reception during the currentnetwork re-entry procedure (‘omit SBC-REQ/RSP management message duringthe current network re-entry processing’). When the second bit (bit #1)has a value of 1, it indicates that it is possible to omit the PKM-REQmessage transmission and PKM-RSP message reception during the currentnetwork re-entry procedure (‘omit PKM-REQ/RSP management messages duringcurrent network re-entry processing’). When the third bit (bit #2) has avalue of 1, it indicates that it is possible to omit the REG-REQ messagetransmission and REG-RSP message reception during the current networkre-entry procedure (‘omit REG-REQ/RSP management messages during currentnetwork re-entry processing’). When the fourth bit (bit #3) has a valueof 1, it indicates that it is possible to omit transmission/reception ofnetwork address acquisition messages during the current network re-entryprocedure (‘omit Network Address Acquisition management messages duringcurrent network re-entry processing’). When the fifth bit (bit #4) has avalue of 1, it indicates that it is possible to omittransmission/reception of time information acquisition messages duringthe current network re-entry procedure (‘omit Time of Day Acquisitionmanagement messages during current network re-entry processing’). Whenthe sixth bit (bit #5) has a value of 1, it indicates that it ispossible to omit transmission/reception of TFTP messages during thecurrent network re-entry procedure (‘omit TFTP management messagesduring current network re-entry processing’).

Upon receiving the RNG-RSP message from the BS 920, the MS 900 performsthe following steps of the network re-entry process in accordance withthe bit values of the Response Type of the RNG-RSP message. For example,when the first bit (bit #0) from among the bits of the Response Type hasa value of 1, the SBC-REQ message transmission of step 921 and SBC-RSPmessage reception of step 923 are omitted. When the second bit (bit #1)from among the bits of the Response Type has a value of 1, the PKM-REQmessage transmission of step 925 and PKM-RSP message reception of step929 are omitted. When the third bit (bit #2) from among the bits of theResponse Type has a value of 1, the REG-REQ message transmission of step931 and REG-RSP message reception of step 933 are omitted.

When the second bit (bit #1) from among the bits of the Response Typehas a value of 0, the PKM-REQ message transmission in step 925 andPKM-RSP message reception in step 929 must be performed, so that the BS920 must perform a privacy key reissue step in step 927 for refreshingthe privacy key value together with the ASA server 940. Here, thereduced network re-entry process refers to a process when the first bit(bit #0) through the third bit (bit #2) of the Response Type of theRNG-RSP message are set to have a value of 1, such that the networkre-entry procedure includes only the ranging procedure, which includesthe RNG-REQ message transmission steps and the RNG-RSP message receptionstep, while omitting all of the SBC-REQ message transmission and SBC-RSPmessage reception steps, the PKM-REQ message transmission and PKM-RSPmessage reception steps and the REG-REQ message transmission and REG-RSPmessage reception steps.

When packet data to be transmitted from the BS to the MS without requestoccur, the BS must page the MS and transmit the packet data to the MS,which case will be described with reference to FIG. 10.

FIG. 10 is a signal flow diagram of a network re-entry process when theBS pages the MS in the idle state according to an embodiment of thepresent invention. Referring to FIG. 10, the MS 1000 stays in the idlestate in step 1011. If the ASA server 1040 detects a paging to the MS1000, the ASA server 1040 transmits a Mobile Paging Request(MOB-PAG-REQ) message to the BS 1020 in step 1013. Upon receiving theMOB-PAG-REQ message from the ASA server 1040, the BS 1020 transmits aMOB-PAG-ADV message to the MS 1000 in step 1014. Herein, the MOB-PAG-ADVmessage is a message newly proposed by the present invention and isgenerated by modifying the format of the MOB-PAG-ADV message of thetypical IEEE 802.16e communication system. Alternatively, theMOB-PAG-ADV message according to an embodiment of the present inventionmay be generated with a totally new format, instead of being generatedby modifying the format of the MOB-PAG-ADV message of the typical IEEE802.16e communication system.

FIG. 13 illustrates a table of the MOB-PAG-ADV message according to anembodiment of the present invention. Referring to FIG. 13, theMOB-PAG-ADV message includes an IE named RCS_INDICATOR, which indicatesif the RCS is required. When the RCS_INDICATOR has a bit value of 1, itindicates that the RCS is required.

Referring back to FIG. 10, upon receiving the MOB-PAG-ADV message fromthe BS 1020, the MS 1000 sets the RCS Request and the Request Type ofthe RNG-REQ message in accordance with the bit value of theRCS_INDICATOR in the MOB-PAG-ADV message and then transmits the RNG-REQmessage to the BS 1020 in step 1015. The RCS Request and the RequestType of the RNG-REQ message have been already described above, sorepetition thereof will be omitted here.

Upon receiving the RNG-REQ message from the MS 1000, the BS 1020transmits a Mobile Paging Response (MOB-PAG-RSP) message to the ASAserver 1040, as a response to the MOB-PAG-REQ message, in step 1017.

Upon receiving the MOB-PAG-RSP message from the BS 1020, the ASA server1040 transmits an SIR-RSP message carrying the SIR of the MS 1000 to theBS 1020 in an unsolicited manner in step 1019.

Upon receiving the SIR-RSP message from the ASA server 1040, the BS 1020transmits an RNG-RSP message including the RCS Response and the ResponseType to the MS 1000 as a response to the RNG-REQ message in step 1021.The RCS Response and the Response Type of the RNG-RSP message have beenalready described above, so repetition thereof will be omitted here. Theprocess of network re-entry after reception of the RNG-RSP message isprogressed in accordance with the RCS Response and the Response Type ofthe RNG-RSP message.

According to the present invention, as described above, when an MStransitions into the idle state, the MS stores the SIR, which is finalsession information in the active state before the idle state and thenperforms a network re-entry process, such that the MS can achieve fastnetwork re-entry, which omits unnecessary steps by using the SIR. Suchfast network re-entry, omitting unnecessary messagetransmission/reception steps, as described above, reduces the messagesignaling load. Therefore, the present invention can improve the entiresystem performance.

While the present invention has been shown and described with referenceto certain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the presentinvention as defined by the appended claims.

1. A method for fast network re-entry of a mobile station in a broadbandwireless access communication system, the method comprising the stepsof: transmitting a first message requesting fast network re-entry to abase station when the mobile station detects that it is necessary toperform network re-entry to the base station in an idle state in whichthe mobile station stores final session information of a previous activestate; receiving a second message approving the fast network re-entryfrom the base station; and performing the fast network re-entry with thebase station.
 2. The method as claimed in claim 1, wherein the firstmessage includes first information indicating that the network re-entryto be performed is the fast network re-entry, and second informationindicating processes that must be omitted during the fast networkre-entry from among a plurality of processes performed in a conventionalnetwork re-entry.
 3. The method as claimed in claim 2, wherein thesecond message includes third information indicating approval of thefast network re-entry, and fourth information indicating processes thatmust be omitted during the fast network re-entry from among a pluralityof processes performed in a conventional network re-entry.
 4. The methodas claimed in claim 3, wherein the step of performing the fast networkre-entry with the base station comprises omitting the processes fromamong the plurality of processes performed in the conventional networkre-entry based on the fourth information; and performing only remainingprocesses.
 5. The method as claimed in claim 1, wherein the firstmessage is a ranging request message including first information andsecond information, the first information indicating that the networkre-entry is the fast network re-entry, the second information indicatingprocesses that must be omitted during the fast network re-entry fromamong a subscriber station basic capability negotiation process, aprivacy key management process, a network address acquisition process, atime information acquisition process, and a TFTP (Trivial File TransferProtocol) process, which are performed in a conventional networkre-entry.
 6. The method as claimed in claim 5, wherein the secondmessage is a ranging response message including third information andfourth information, the third information indicating approval of thefast network re-entry, the fourth information indicating processes whichmust be omitted during the fast network re-entry from among thesubscriber station basic capability negotiation process, the privacy keymanagement process, the network address acquisition process, the timeinformation acquisition process, and the TFTP process, which areperformed in the conventional network re-entry.
 7. The method as claimedin claim 6, wherein the step of performing the fast network re-entrywith the base station, comprises: omitting processes from among thesubscriber station basic capability negotiation process, the privacy keymanagement process, the network address acquisition process, the timeinformation acquisition process, and the TFTP process, based on thefourth information; and performing only remaining processes.
 8. A methodfor fast network re-entry of a mobile station in a broadband wirelessaccess communication system including the mobile station, a serving basestation that provides service to the mobile station, a target basestation, which is different from the serving base station, and an ASA(Authentication and Service Authorization) server connected to thetarget base station, the method comprising the steps of: storing finalsession information by the mobile station when transitioning into anidle state; transmitting the final session information to the targetbase station so that the target base station and the ASA server storethe final session information, when the mobile station detects thathandover from the serving base station to the target base station isnecessary, after the mobile station stores the final sessioninformation; transmitting a first message requiring fast networkre-entry to the target base station; receiving a second messageapproving the fast network re-entry from the target base station; andperforming the fast network re-entry with the target base station. 9.The method as claimed in claim 8, wherein the first message includesfirst information indicating that the network re-entry is the fastnetwork re-entry, and second information indicating processes that mustbe omitted during the fast network re-entry from among a plurality ofprocesses performed in a conventional network re-entry.
 10. The methodas claimed in claim 9, wherein the second message includes thirdinformation indicating approval of the fast network re-entry, and fourthinformation indicating the processes that must be omitted during thefast network re-entry from among the plurality of processes performed inthe conventional network re-entry.
 11. The method as claimed in claim10, wherein the step of performing the fast network re-entry with thetarget base station, comprises: omitting processes from among theplurality of processes performed in the conventional network re-entrybased on the fourth information; and performing only remainingprocesses.
 12. The method as claimed in claim 8, wherein the firstmessage is a ranging request message including first information andsecond information, the first information indicating that the networkre-entry is the fast network re-entry, the second information indicatingprocesses which must be omitted during the fast network re-entry fromamong a subscriber station basic capability negotiation process, aprivacy key management process, a network address acquisition process, atime information acquisition process and a TFTP (Trivial File TransferProtocol) process, which are performed in a conventional networkre-entry.
 13. The method as claimed in claim 12, wherein the secondmessage is a ranging response message including third information andfourth information, the third information indicating approval of thefast network re-entry, the fourth information indicating the processesthat must be omitted during the fast network re-entry from among thesubscriber station basic capability negotiation process, the privacy keymanagement process, the network address acquisition process, the timeinformation acquisition process and the TFTP process, which areperformed in the conventional network re-entry.
 14. The method asclaimed in claim 13, wherein the step of performing the fast networkre-entry with the target base station, comprises: omitting processesfrom among the subscriber station basic capability negotiation process,the privacy key management process, the network address acquisitionprocess, the time information acquisition process and the TFTP process,which are performed in the conventional network re-entry, based on thefourth information; and performing only remaining processes.
 15. Amethod for fast network re-entry of a base station in a broadbandwireless access communication system, the method comprising the stepsof: receiving a first message requiring fast network re-entry from amobile station that is in an idle state during which the mobile stationstores final session information of a previous active state;authenticating the first message using final session information of themobile station that is previously stored in the base station;transmitting a second message approving the fast network re-entry to themobile station, after the first message is authenticated; and performingthe fast network re-entry with the mobile station.
 16. The method asclaimed in claim 15, wherein the first message includes firstinformation indicating that the network re-entry is the fast networkre-entry, and second information indicating processes that must beomitted during the fast network re-entry from among a plurality ofprocesses performed in a conventional network re-entry.
 17. The methodas claimed in claim 16, wherein the second message includes thirdinformation indicating approval of the fast network re-entry, and fourthinformation indicating the processes that must be omitted during thefast network re-entry from among the plurality of processes performed inthe conventional network re-entry.
 18. The method as claimed in claim17, wherein the step of performing the fast network re-entry with themobile station, comprises: omitting processes from among the pluralityof processes performed in the conventional network re-entry, based onthe fourth information; and performing only remaining processes.
 19. Themethod as claimed in claim 15, wherein the first message is a rangingrequest message including first information and second information, thefirst information indicating that the network re-entry is the fastnetwork re-entry, the second information indicating processes which mustbe omitted during the fast network re-entry from among a subscriberstation basic capability negotiation process, a privacy key managementprocess, a network address acquisition process, a time informationacquisition process, and a TFTP (Trivial File Transfer Protocol)process, which are performed in a conventional network re-entry.
 20. Themethod as claimed in claim 19, wherein the second message is a rangingresponse message including third information and fourth information, thethird information indicating approval of the fast network re-entry, thefourth information indicating the processes that must be omitted duringthe fast network re-entry from among the subscriber station basiccapability negotiation process, the privacy key management process, thenetwork address acquisition process, the time information acquisitionprocess, and the TFTP process, which are performed in the conventionalnetwork re-entry.
 21. The method as claimed in claim 20, wherein thestep of performing the fast network re-entry together with the mobilestation, comprises: omitting processes from among the subscriber stationbasic capability negotiation process, the privacy key managementprocess, the network address acquisition process, the time informationacquisition process and the TFTP process, which are performed in theconventional network re-entry, based on the fourth information; andperforming only remaining processes.
 22. A method for fast networkre-entry in a broadband wireless access communication system, the methodcomprising the steps of: transmitting a first message requiring fastnetwork re-entry from a mobile station to a base station, when themobile station detects that it is necessary to perform network re-entryto the base station in an idle state during which the mobile stationstores final session information of a previous active state; receivingthe first message by the base station; authenticating the first messageby the base station using final session information of the mobilestation that is previously stored in the base station; transmitting asecond message approving the fast network re-entry to the mobilestation, the first message is authenticated; and performing the fastnetwork re-entry by the mobile station and the base station.
 23. Themethod as claimed in claim 22, wherein the first message includes firstinformation indicating that the network re-entry to be performed is thefast network re-entry, and second information indicating processes thatmust be omitted during the fast network re-entry from among a pluralityof processes performed in a conventional network re-entry.
 24. Themethod as claimed in claim 23, wherein the second message includes thirdinformation indicating approval of the fast network re-entry, and fourthinformation indicating the processes that must be omitted during thefast network re-entry from among the plurality of processes performed inthe conventional network re-entry.
 25. The method as claimed in claim24, wherein the step of performing the fast network re-entry by themobile station together with the base station, comprises: omittingprocesses from among the plurality of processes performed in theconventional network re-entry based on the fourth information; andperforming only remaining processes.
 26. The method as claimed in claim22, wherein the first message is a ranging request message includingfirst information and second information, the first informationindicating that the network re-entry to be performed is the fast networkre-entry, the second information indicating processes that must beomitted during the fast network re-entry from among a subscriber stationbasic capability negotiation process, a privacy key management process,a network address acquisition process, a time information acquisitionprocess, and a TFTP (Trivial File Transfer Protocol) process, which areperformed in a conventional network re-entry.
 27. The method as claimedin claim 26, wherein the second message is a ranging response messageincluding third information and fourth information, the thirdinformation indicating approval of the fast network re-entry, the fourthinformation indicating processes that must be omitted during the fastnetwork re-entry from among the subscriber station basic capabilitynegotiation process, the privacy key management process, the networkaddress acquisition process, the time information acquisition process,and the TFTP process, which are performed in the conventional networkre-entry.
 28. The method as claimed in claim 27, wherein the step ofperforming the fast network re-entry by the mobile station together withthe base station, comprises: omitting processes from among thesubscriber station basic capability negotiation process, the privacy keymanagement process, the network address acquisition process, the timeinformation acquisition process, and the TFTP process, which areperformed in the conventional network re-entry, based on the fourthinformation; and performing only remaining processes.
 29. A method forfast network re-entry in a broadband wireless access communicationsystem that includes the mobile station, a serving base station thatprovides service to the mobile station, a target base station, which isdifferent from the serving base station, and an ASA (Authentication andService Authorization) server connected to the target base station, themethod comprising the steps of: transmitting final session informationfrom the mobile station to the target base station so that the targetbase station and the ASA server store the final session information,when the mobile station detects that handover from the serving basestation to the target base station is necessary, after the mobilestation stores the final session information while transitioning into anidle state; receiving the final session information in the target basestation; storing the final session information in the target basestation; transmitting a first message requiring the fast networkre-entry to the target base station; receiving the first message by thetarget base station; authenticating the first message by the target basestation using final session information of the mobile station stored inadvance in the target base station; transmitting a second messageapproving the fast network re-entry to the mobile station, afterauthenticating the first message; and performing the fast networkre-entry by the mobile station and the target base station.
 30. Themethod as claimed in claim 29, wherein the first message includes firstinformation indicating that the network re-entry to be performed is thefast network re-entry, and second information indicating processes thatmust be omitted during the fast network re-entry from among a pluralityof processes performed in a conventional network re-entry.
 31. Themethod as claimed in claim 30, wherein the second message includes thirdinformation indicating approval of the fast network re-entry, and fourthinformation indicating the processes that must be omitted during thefast network re-entry from among the plurality of processes performed inthe conventional network re-entry.
 32. The method as claimed in claim31, wherein the step of performing the fast network re-entry by themobile station together with the target base station comprises: omittingprocesses from among the plurality of processes performed in theconventional network re-entry, based on the fourth information; andperforming only remaining processes.
 33. The method as claimed in claim29, wherein the first message is a ranging request message includingfirst information and second information, the first informationindicating that the network re-entry to be performed is the fast networkre-entry, the second information indicating processes that must beomitted during the fast network re-entry from among a subscriber stationbasic capability negotiation process, a privacy key management process,a network address acquisition process, a time information acquisitionprocess, and a TFTP (Trivial File Transfer Protocol) process, which areperformed in a conventional network re-entry.
 34. The method as claimedin claim 33, wherein the second message is a ranging response messageincluding third information and fourth information, the thirdinformation indicating approval of the fast network re-entry, the fourthinformation indicating processes that must be omitted during the fastnetwork re-entry from among the subscriber station basic capabilitynegotiation process, the privacy key management process, the networkaddress acquisition process, the time information acquisition process,and the TFTP process, which are performed in the conventional networkre-entry.
 35. The method as claimed in claim 34, wherein the step ofperforming the fast network re-entry by the mobile station together withthe target base station comprises: omitting processes from among thesubscriber station basic capability negotiation process, the privacy keymanagement process, the network address acquisition process, the timeinformation acquisition process, and the TFTP process, which areperformed in the conventional network re-entry, based on the fourthinformation; and performing only remaining processes.
 36. A system forfast network re-entry in a broadband wireless access communicationsystem, the system comprising: a base station; and a mobile station fortransmitting a first message requiring fast network re-entry to the basestation when the mobile station detects that it is necessary to performnetwork re-entry to the base station in an idle state during which themobile station stores final session information of a previous activestate, the mobile station performing the fast network re-entry togetherwith the base station when receiving a second message approving the fastnetwork re-entry from the base station, wherein the base stationreceives the first message, authenticates the first message using finalsession information of the mobile station that is previously stored inthe base station, transmits the second message to the mobile station,after authenticating the first message, and performs the fast networkre-entry with the mobile station.
 37. The system as claimed in claim 36,wherein the first message comprises: first information indicating thatthe network re-entry to be performed is the fast network re-entry; andsecond information indicating processes that must be omitted during thefast network re-entry from among a plurality of processes performed in aconventional network re-entry.
 38. The system as claimed in claim 37,wherein the second message comprises: third information indicatingapproval of the fast network re-entry; and fourth information indicatingthe processes that must be omitted during the fast network re-entry fromamong the plurality of processes performed in the conventional networkre-entry.
 39. The system as claimed in claim 38, wherein the step ofperforming the fast network re-entry by the mobile station together withthe base station comprises: omitting processes from among the pluralityof processes performed in the conventional network re-entry, based onthe fourth information; and performing only remaining processes.
 40. Thesystem as claimed in claim 36, wherein the first message is a rangingrequest message including first information and second information, thefirst information indicating that the network re-entry to be performedis the fast network re-entry, the second information indicatingprocesses that must be omitted during the fast network re-entry fromamong a subscriber station basic capability negotiation process, aprivacy key management process, a network address acquisition process, atime information acquisition process, and a TFTP (Trivial File TransferProtocol) process, which are performed in a conventional networkre-entry.
 41. The system as claimed in claim 40, wherein the secondmessage is a ranging response message including third information andfourth information, the third information indicating approval of thefast network re-entry, the fourth information indicating the processesthat must be omitted during the fast network re-entry from among thesubscriber station basic capability negotiation process, the privacy keymanagement process, the network address acquisition process, the timeinformation acquisition process, and the TFTP process, which areperformed in the conventional network re-entry.
 42. The system asclaimed in claim 41, wherein the fast network re-entry is performed byomitting processes from among the subscriber station basic capabilitynegotiation process, the privacy key management process, the networkaddress acquisition process, the time information acquisition process,and the TFTP process, which are performed in the conventional networkre-entry, based on the fourth information, and performing only remainingprocesses.
 43. A system for fast network re-entry in a broadbandwireless access communication system, the system comprising: a targetbase station; and a mobile station for storing final session informationwhen transitioning into an idle state, transmitting the final sessioninformation to the target base station, such that the target basestation and an ASA (Authentication and Service Authorization) serverstore the final session information, when the mobile station detectsthat handover from a serving base station to the target base station isnecessary after the mobile station stores the final session information,transmitting a first message requiring fast network re-entry to thetarget base station, and performing the fast network re-entry with thetarget base station, when receiving a second message approving the fastnetwork re-entry from the target base station; wherein the target basestation receives and stores the final session information, authenticatesthe first message using final session information of the mobile stationstored in advance in the target base station, transmits the secondmessage to the mobile station, after authenticating the first message,and performs the fast network re-entry together with the mobile station.44. The system as claimed in claim 43, wherein the first messagecomprises: first information indicating that the network re-entry to beperformed is the fast network re-entry; and second informationindicating processes that must be omitted during the fast networkre-entry from among a plurality of processes performed in a conventionalnetwork re-entry.
 45. The system as claimed in claim 44, wherein thesecond message comprises: third information indicating approval of thefast network re-entry; and fourth information indicating processes thatmust be omitted during the fast network re-entry from among theplurality of processes performed in the conventional network re-entry.46. The system as claimed in claim 45, wherein, when the mobile stationand the target base station perform the fast network re-entry, processesfrom among the plurality of processes performed in the conventionalnetwork re-entry are omitted based on the fourth information and onlyremaining processes are performed.
 47. The system as claimed in claim43, wherein the first message is a ranging request message includingfirst information and second information, the first informationindicating that the network re-entry to be performed is the fast networkre-entry, the second information indicating processes that must beomitted during the fast network re-entry from among a subscriber stationbasic capability negotiation process, a privacy key management process,a network address acquisition process, a time information acquisitionprocess, and a TFTP (Trivial File Transfer Protocol) process, which areperformed in a conventional network re-entry.
 48. The system as claimedin claim 47, wherein the second message is a ranging response messageincluding third information and fourth information, the thirdinformation indicating approval of the fast network re-entry, the fourthinformation indicating the processes that must be omitted during thefast network re-entry from among the subscriber station basic capabilitynegotiation process, the privacy key management process, the networkaddress acquisition process, the time information acquisition process,and the TFTP process, which are performed in the conventional networkre-entry.
 49. The system as claimed in claim 48, wherein, when themobile station and the target base station perform the fast networkre-entry, processes from among the subscriber station basic capabilitynegotiation process, the privacy key management process, the networkaddress acquisition process, the time information acquisition process,and the TFTP process, which are performed in the conventional networkre-entry, are omitted based on the fourth information; and onlyremaining processes are performed.
 50. A method for fast networkre-entry of a base station in a broadband wireless access communicationsystem, the method comprising the steps of: transmitting to a mobilestation in an active state a deregistration command message to requestfor transition into an idle state, wherein the deregistration commandmessage includes session information for a fast network re-entry;receiving a ranging request message from the mobile station to performthe network re-entry after the mobile station transit into the activestate; transmitting to the mobile station a ranging response messagethat includes the session information represents whether each networkre-entry process among network re-entry procedure is omitted orrequired.
 51. The method as claimed in claim 50, wherein the sessioninformation in the deregistration command message represents servicesfor the mobile station and operational information to be retained oromitted.
 52. The method as claimed in claim 50, wherein the networkre-entry procedure includes a subscriber station basic capabilitynegotiation process, a privacy key management process, a network addressacquisition process, a time information acquisition process, and a TFTP(Trivial File Transfer Protocol) process, which are performed in aconventional network re-entry.